The most important problem nowadays for hetero-bone implant is immunological defensive reaction occurring in the biological body. Previously many researchers dealt with this by different methods, such as freezing, boiling or chemical soaking, but the immuno-defensive reaction, evoked by the hetero-bone implant, could not be avoided by these methods. In 1988, Mittelmeier et al. used high-temperature heating to sinter bovine bone in order to remove all the organic components that might cause immuno-defensive reaction, whereas the biocompatible inorganic components remained. Because the major inorganic substance in bone is Ca.sub.10 (PO.sub.4).sub.6 (OH).sub.2 (hydroxyapatite; HAP), after the removal of organic components the remnant mineral is like a crystalline mold of metallurgic powder. In the continuous heating process of the remnant mineral, a strong ceramic sinter can be obtained. Because bovine bone is cancellous, it has a natural porous structure, and the porosity can be as high as 70 vol %. Therefore, a natural porous bioceramic material, mainly composed of HAP, can be obtained by using this method. At the present time this material has been widely used in clinical bone surgery as a bone defect filling material.
The major inorganic component in raw cancellous bone is HAP, which is the same as in human bone. Consequently, it has a good biocompatibility. However, also due to the similar compositions, which reduce the bioactivity. In recent years, some researchers added highly soluable .beta.-tricalcium phosphate (Ca.sub.3 (PO.sub.4).sub.2 ; .beta.-TCP) in HAP to form a biphasic (HAP/.beta.-TCP) bioceramic material. In animal experiments, implant of biphasic bioceramic material in bone tissue demonstrated a better clinical effect than pure HAP or pure .beta.-TCP.